Patent GB-901586-A (GB)
Abstract: 901,586. Fluid-pressure servomotor-control systems. ROLLS-ROYCE Ltd. Dec. 16, 1958 [Dec. 30, 1957], No. 40355/57. Class 135. [Also in Group XXVI] A by-pass gas-turbine jet-propulsion engine comprises a series-flow arrangement of a lowpressure (L.P.) compressor 10, Fig. 1, a highpressure (H.P.) compressor 11, combustion equipment 12, and a multi-stage turbine 13; the turbine exhaust gases flow to a propulsion nozzle 17. The by-pass passage 18, which receives a proportion of air from the L.P. compressor 10, either opens directly to atmosphere via an adjustable nozzle 18b or enters the turbine exhaust stream. The H.P. compressor 11 is provided with adjustable stator blades 11b to facilitate matching of the pressures of by-pass air and exhaust gases; when such matching is required the compression ratios of the L.P. and H.P. compressors are selected to be about 2.2 to 1 and 6.1, respectively. The blades 11b and the nozzle 18b are adjusted by rams 25, 24, respectively, controlled by either the L.P. or H.P. compressor speed; such adjustment also provides extra thrust to be obtained, e.g. during aircraft takeoff. As the area of the nozzle 18b is reduced so the blades 11b are moved away from their normal position in a negative sense to accommodate the increased mass flow through the compressor. Stalling of the H.P. compressor 11 may be avoided at starting and run-up by giving the blades 11b a decreasing positive setting as the compressor speed increases towards a given value at which stalling does not occur; during this operation the nozzle 18b is not adjusted. Each ram 24, 25, which may incorporate a retractable stop, not shown, may also be constructed as described in Specification 704,936. Each ram may comprise a spring-loaded differential piston, the two ends of which are interconnected by a restrictor whilst the smaller end is connected to a fluid-pressure source and the other end has a bleed-off valve responsive to a signal from an hydraulic governor pump 26 transmitted through a pipe 32 so giving proportional control. Where a separate hydraulic governor is used the pump 26 simply delivers fuel to the combustion equipment 12 and supplies operating fluid to the rams 24, 25 by pipes 30, 31. During starting run-up and normal operation the stops of rams 24 are in position and as the throttle 29 is opened the rams 25 move the blades from a positive setting suitable for starting until they abut their stops. With the throttle 29 set for maximum power extra thrust is obtained by operating a lever 33 to withdraw the stops of both rams which latter will then be speed-controlled whereupon the nozzle 18b is progressively closed and the blades 11b moved to a negative setting. The lever 33 may be connected to the throttle 29. In a modification, no adjustment of the stator blades is provided, the lever 33 operating the stops of rams 24 and increasing the speed setting of the hydraulic governor. When the by-pass passage 18a, Fig. 4, opens into the turbine exhaust stream the outlet from the passage is formed with a series of flattened nozzles 40 terminating in openings 41 with corrugated peripheries and each nozzle is provided with a pivoted valve 42 movable by rams between open and closed positions. The valves 42 may be connected for conjoint operation. Specification 852,829 also is referred to.